TiO2 NP & catalyst for the synthesis of benzopyrano benzopyranone and xanthenol in water

Many results of pharmacological studies have unveiled that, chromenes (2H-1-benzopyran derivatives) and xanthenes (dibenzopyrans) have useful biological activities. However, during the last few decades, metal oxide nanoparticles (NPs) are being extensively studied due to their significant physical and chemical abilities, including their role as heterogeneous catalysts. The aim of this review is to increase the catalytic efficiency of the synthesized TiO2 NPs which is supported by carbon nanotubes (CNTs) for the sake of preparation of these heterocyclic scaffolds.

This article is focuses on a green and efficient method of synthesis of [1]benzopyrano[b][1]benzopyran-6-ones and xanthenols through a pseudo three-component reaction of salicylaldehydes with active methylene compounds including 4-hydroxycoumarin (4-hydroxy-2H-1- benzopyran-2-one) or 3,4-methylenedioxyphenol, in a molar ratio of 1:2. At room temperature, the reaction was carried out in the presence of the synthesized TiO2-CNTs as a catalyst in aqueous medium. With the help of the scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and the energy dispersive X-ray detector (EDX) techniques, the synthesized catalysts were fully characterized. All of the synthesized compounds were distinguished by IR, 1H and 13C-NMR spectroscopy, as well as elemental analyses.Sixteen target compounds containing [1]benzopyrano[b][1]benzopyran-6-ones and xanthenols were also successfully synthesized in high yields (around approximately 92-98%) within short reaction times (1.5-3 h).

In this study, TiO2-CNTs were used as efficient recyclable catalysts for the synthesis of [1]benzopyrano[b][1]benzopyran-6-ones and xanthenols by the pseudo three-component reaction of salicylaldehydes along with active methylene compounds including 4-hydroxycoumarin (4-hydroxy-2H- 1-benzopyran-2-one) or 3,4-methylenedioxyphenol. The introduced method has been proven mild, environmental-friendly and effective enough to provide outputs product in high yields and in short time periods.